linux-kernel - Re: [PATCH v3 1/7] dt-bindings: input: syna,rmi4: document syna,pdt-fallback-desc

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Message-ID: <fb176bbf-5e31-4e72-8201-4a2fc4d57ef5@linaro.org>
Date: Sat, 29 Mar 2025 10:56:27 +0100
From: Caleb Connolly <caleb.connolly@...aro.org>
To: David Heidelberg <david@...t.cz>, Krzysztof Kozlowski <krzk@...nel.org>
Cc: Dmitry Torokhov <dmitry.torokhov@...il.com>, Rob Herring
 <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>,
 Conor Dooley <conor+dt@...nel.org>, "Jason A. Donenfeld" <Jason@...c4.com>,
 Matthias Schiffer <matthias.schiffer@...tq-group.com>,
 Vincent Huang <vincent.huang@...synaptics.com>, linux-input@...r.kernel.org,
 devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
 phone-devel@...r.kernel.org, ~postmarketos/upstreaming@...ts.sr.ht
Subject: Re: [PATCH v3 1/7] dt-bindings: input: syna,rmi4: document
 syna,pdt-fallback-desc



On 3/28/25 23:45, David Heidelberg wrote:
> On 26/03/2025 11:26, Caleb Connolly wrote:
>>
>>
>> On 3/26/25 07:57, Krzysztof Kozlowski wrote:
>>> On 25/03/2025 14:23, Caleb Connolly wrote:
>>>>
>>>>
>>>> On 3/25/25 08:36, Krzysztof Kozlowski wrote:
>>>>> On 24/03/2025 19:00, David Heidelberg wrote:
>>>>>> On 10/03/2025 10:45, Krzysztof Kozlowski wrote:
>>>>>>> On Sat, Mar 08, 2025 at 03:08:37PM +0100, David Heidelberg wrote:
>>>>>>>> From: Caleb Connolly <caleb.connolly@...aro.org>
>>>>>>>>
>>>>>>>> This new property allows devices to specify some register values 
>>>>>>>> which
>>>>>>>> are missing on units with third party replacement displays. These
>>>>>>>> displays use unofficial touch ICs which only implement a subset 
>>>>>>>> of the
>>>>>>>> RMI4 specification.
>>>>>>>
>>>>>>> These are different ICs, so they have their own compatibles. Why 
>>>>>>> this
>>>>>>> cannot be deduced from the compatible?
>>>>>>
>>>>>> Yes, but these identify as the originals.
>>>>>
>>>>>
>>>>> It does not matter how they identify. You have the compatible for 
>>>>> them.
>>>>> If you cannot add compatible for them, how can you add dedicated
>>>>> property for them?
>>>>
>>>> Hi Krzysztof,
>>>>
>>>> There are an unknown number of knock-off RMI4 chips which are sold in
>>>> cheap replacement display panels from multiple vendors. We suspect
>>>> there's more than one implementation.
>>>>
>>>> A new compatible string wouldn't help us, since we use the same DTB on
>>>> fully original hardware as on hardware with replacement parts.
>>>>
>>>> The proposed new property describes configuration registers which are
>>>> present on original RMI4 chips but missing on the third party ones, the
>>>> contents of the registers is static.
>>>
>>>
>>> So you want to add redundant information for existing compatible, while
>>> claiming you cannot deduce it from that existing compatible... Well,
>>> no.. you cannot be sure that only chosen boards will have touchscreens
>>> replaced, thus you will have to add this property to every board using
>>> this compatible making it equal to the compatible and we are back at my
>>> original comment. This is deducible from the compatible. If not the new
>>> one, then from old one.
>>
>> hmm I see, so instead we should add a compatible for the specific 
>> variant (S3320 or something) of RMI4 in this device and handle this in 
>> the driver? I think that makes sense.
> 
> Agree, preparing it for v4. So far proposing `compatible = "syna,rmi4- 
> s3706b-i2c", "syna,rmi4-i2c"` (as S3706B is written in the commit and 
> search confirms it for OP6/6T).

ack, sounds good!
> 
> David>
>>>
>>> Best regards,
>>> Krzysztof
>>
> 

-- 
Caleb (they/them)